What is a single replacement equation?

Replacements are used in several chemical processes. In compounds, more reactive components replace less reactive ones, and replacement reactions are the name for these reactions.

REPLACEMENT REACTION

When elements in a compound swap locations, this is called a replacement reaction. Ions (electrically charged counterparts of atoms) or ionic compounds are involved in this sort of reaction.

In most cases, a more reactive component substitutes a less reactive element, and the less reactive component is liberated from the combination.

SINGLE REPLACEMENT REACTION

A single replacement reaction happens whenever one element replaces the other in a single component. The general expression for this sort of reaction is:

When potassium combines with water, it is an example of a single substitution reaction. Potassium hydroxide, a white solid chemical, is formed, and hydrogen gas is released.

According to the expression, a potassium ion substitutes one of the hydrogen atoms within every water molecule in this process. Because potassium is a powerful oxidizing group 1 alkali metal, it reacts violently with water.

HOW TO BALANCE A SINGLE REPLACEMENT REACTION:

A single replacement reaction's expression is balanced similarly to any other equation. Coefficients are placed in the front of chemical formulations to ensure that the number of atoms in each element is the same across all sides.

Let's try and understand this with an example:

• We put a multiplier of 2 in front of NaCl because there are 2 Cl atoms upon that left side of the equation and another on the right.

• We now also have two Na atoms here on the right-hand side, but only one is on the left, so we put two next to the Na.

  Na(s) + ZnCl₂(aq) → 2NaCl(aq) + Zn(s)

• The equation is now in equilibrium. On both sides of the equation, there seems to be an equal amount of each element.

CONCLUSION:

• In a single replacement reaction, a single element in a compound is replaced by the other.
• Single-replacement interactions can be predicted using the periodic table or a reactivity sequence.

FAQs:

1. How do you balance a single replacement reaction?

A single replacement reaction's formula is balanced in the very same manner as any other equation. Coefficients are placed in front of chemical formulations to ensure that the number of atoms in each element is the same on both ends.

2. How do you balance an unbalanced reaction?

(i). Count all atom types in the reactants and products.

(ii). To increase the number of atoms or molecules in the components, use coefficients in front of every symbol or formula as needed.

(iii). Steps (i) and (ii) should be repeated until the formula is balanced.

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SOURCES:

A single-replacement reaction, also called a single-displacement reaction, is a reaction in which one element is substituted for another element in a compound. In order to understand the chemistry of a single-replacement reaction, one has to know about the activity series of elements in the periodic table. Elements that are higher in the series have a greater tendency to gain or lose electrons and hence, can easily displace elements that are lower in the series. Both metals and nonmetals participate in replacement reactions [1-5].

General Equation for Single-replacement Reaction

The single-displacement reaction equation is:

A + BC → AC + B

This reaction will proceed if A is more reactive than B. When writing an actual reaction, the reaction must be balanced [1].

A characteristic of a single-replacement reaction is that one cation or anion trades places with another to form a new product. Metals that are more reactive than hydrogen readily dissolve in water. They form hydroxides and release hydrogen gas.

Examples of Single-replacement Reaction

An example of a single-displacement reaction occurs when potassium (K) reacts with water (H2O). A colorless solid compound named potassium hydroxide (KOH) forms, and hydrogen gas (H2) is set free. The equation for the reaction is:

2 K (s) + 2 H2O (l) → 2 KOH + H2 (g)

Consider the following example. Magnesium (Mg) replaces hydrogen (H) in hydrochloric acid (HCl) and forms magnesium chloride (MgCl2) and gaseous hydrogen (H2).

Mg (s) + HCl (aq.) → MgCl2 (s) + H2 (g)

This equation is not balanced. We note that there are two hydrogen and chlorine atoms on the right-hand side of the equation. So, we multiply the compound HCl on the left by 2 and balance the two atoms.

Mg (s) + 2 HCl (aq.) → MgCl2 (s) + H2 (g)

Rules for Prediction of Single-replacement Reaction

The periodic table or an activity series can help to predict whether single-replacement reactions occur. Whether one element will replace another element from a compound can be determined by the relative reactivities of the two elements. A single-replacement reaction will occur when a less reactive element can be replaced by a more reactive element in a compound [2].

1. Halogens

Order of reactivity of the halogens:

More reactive     F2  >  Cl2  >  Br2  >  I2    Less reactive

From this order, one can see that chlorine (Cl2) will replace bromine (Br2) from a bromide compound but cannot replace fluorine (F2) from a fluoride compound.

2. Metals

Order of reactivity of metals:

More reactive    Cu  >  Ag  >  Hg  >  Pt  >  Au    Less reactive

From this order, one can see that copper (Cu) will replace silver (Ag) in an aqueous solution consisting of Ag+ ions but not vice-versa.

Types of Single-replacement Reaction

There are two types of single-replacement reactions [2-4].

1. Cation Replacement

A cation is a positively charged ion or a metal. In this type of reaction, one cation replaces another.

Examples

• Zinc (Zn) can safely dissolve in hydrochloric acid (HCl), releasing hydrogen (H2) gas [1].

Zn (s) + 2 HCl (aq.) → ZnCl2 (s) + H2 (g)

• Copper (Cu) can displace silver (Ag) in an aqueous solution of silver nitrate (AgNO3).

Cu (s) + 2 AgNO3 (aq.) → Cu(NO3)2 (aq.) + 2 Ag (s/ppt.)

2. Anion Replacement

An anion is a negatively charged ion or a nonmetal. In this type of reaction, one anion replaces another.

Examples

• Chlorine (Cl2) will displace the bromine (Br2) in a sodium bromide (NaBr) compound because it is more reactive than bromine [1].

Cl2 (aq.) + 2 NaBr (aq.) → 2 NaCl (aq.) + Br2 (aq.)

• Bromine (Br2) replaces iodine (I2) in a reaction between bromine (Br2) and potassium iodide (KI).

Br2 (aq.) + 2 KI (aq.) → 2 KBr (aq.) + I2 (aq.)

Single-replacement Reactions Examples in Everyday Life

There are a few examples of single-replacement reactions taking place in nature and real life.

• The reaction of saltwater with concrete pillars containing iron forms iron (II) chloride
• Silver reacts with hydrogen sulfide gas that is produced by some industrial processes or as a result of decaying animal or plant materials. The reaction results in silver sulfide and hydrogen gas.

References